The fortune command could not be located because '/usr/games' is not included in the PATH environment variable. You can type full command path (/usr/games/fortune) or simply add /usr/games to PATH variable:

exportPATH=$PATH:/usr/games
fortune

Sample outputs:

Your lucky number has been disconnected.

whereis command

The whereis command is used to locate the binary, source, and manual page files for a command.

whereis command-name
whereisls

Sample outputs:

ls: /bin/ls /usr/share/man/man1/ls.1.gz

whatis command

The whatis command is used display a short description about command. whatis command searches the manual page names and displays the manual page descriptions for a command: